1. Field of the Invention
The invention relates generally to drill bits which have polycrystalline diamond compact (xe2x80x9cPDCxe2x80x9d) cutters thereon. More particularly, the invention relates to drill bits having a particular diameter of PDC cutters.
2. Background Art
Polycrystalline diamond compact (xe2x80x9cPDCxe2x80x9d) cutters have been used in industrial applications including rock drilling and metal machining for many years. In these applications, a compact of polycrystalline diamond (or other superhard material such as cubic boron nitride) is bonded to a substrate material, which is typically a sintered metal-carbide to form a cutting structure. A compact is a polycrystalline mass of diamonds (typically synthetic) that are bonded together to form an integral, tough, high-strength mass.
An example of a rock bit for earth formation drilling using PDC cutters is disclosed in U.S. Pat. No. 5,186,268. FIGS. 1 and 2 from that patent show a rotary drill bit having a bit body 10. The lower face of the bit body 10 is formed with a plurality of blades 17-25, which extend generally outwardly away from a central longitudinal axis of rotation 15 of the drill bit. A plurality of PDC cutters 26 are disposed side by side along the length of each blade. The number of PDC cutters 26 carried by each blade may vary. The PDC cutters 26 are brazed to a stud-like carrier, which may also be formed from tungsten carbide, and is received and secured within a socket in the respective blade.
One of the major factors in determining the longevity of PDC cutters is the strength of the bond between the polycrystalline diamond layer and the sintered metal carbide substrate. For example, analyses of the failure mode for drill bits used for earth formation drilling show that in approximately one-third of the cases, bit failure or wear is caused by delamination of the diamond from the metal carbide surface. It has been previously noted that as the diameter of the PDC cutters increase, the stress on the PDC layer and the metal carbide substrate increases. Because of this, prior art bits have typically been limited to having cutters of diameters of 19 mm. PDC cutters having an cutter diameter of 25 mm or 50 mm have been attempted, but are subject to high failure rates because of the increase in shear stress accompanying the larger cutter diameter.
A PDC cutter may be formed by placing a cemented carbide substrate into the container of a press. A mixture of diamond grains or diamond grains and catalyst binder is placed atop the substrate and compressed under high pressure, high temperature conditions. In so doing, metal binder migrates from the substrate and passes through the diamond grains to promote a sintering of the diamond grains. As a result, the diamond grains become bonded to each other to form the diamond layer, and the diamond layer is subsequently bonded to the substrate, which is typically a planar surface. The substrate is often a metalcarbide composite material, such as tungsten carbide.
The deposited diamond layer is often referred to as the xe2x80x9cdiamond table,xe2x80x9d or xe2x80x9cabrasive layer.xe2x80x9d Correspondingly, the xe2x80x9cdiamond table thicknessxe2x80x9d is defined as the thickness (by industry practice usually measured in inches) of the diamond table on the substrate. Furthermore, the xe2x80x9cexposurexe2x80x9d (by industry practice usually measured in millimeters (xe2x80x9cmmxe2x80x9d)) is defined as the portion of the diameter of the cutter which extends past the blade in the direction that the bit drills. Typically, diamond table thickness is limited by the stresses on the diamond table at the interface between the diamond and the substrate. Too thick of a diamond table may result in stress that can cause the cutter to shear from the bit body, or may result in brittle failure of the diamond table. Typical prior art diamond table thicknesses range from 0.090 inches to 0.120 inches. Typical prior art exposures are less than 10.0 mm.
As stated above, many prior art PDC cutters have the diamond table bonded to a substrate having a planar layer. However, in an attempt to reduce the inherent stresses present at the PDC/metal carbide interface, several prior art systems have incorporated substrates having a non-planar geometry to form a non-planar interface. U.S. Pat. No. 5,494,477 discloses such a non-planar interface. FIG. 3 illustrates one embodiment of a non-planar interface. In use, as PDC cutter 110 wears, wear plane 16 (which represents the surface providing cutting action) slowly progresses towards the center of the PDC cutter 110.
A second system using a non-planar interface is disclosed in U.S. Pat. No. 5,662,720. In this system, the surface topography of the substrate system is altered to create an xe2x80x9cegg-cartonxe2x80x9d appearance. This is shown in FIG. 4. The use of an xe2x80x9cegg-cartonxe2x80x9d shape allows the stress associated with the cutting to be distributed over a larger surface area, thereby reducing delamination of the diamond table from the substrate.
As stated above, the most significant problem with PDC cutters arises from the creation of internal stresses within the diamond layer itself, which can result in a fracturing of the layer. The stresses result from difference in thermal properties of the diamond and the substrate, and are distributed according to the size, geometry and physical properties of the substrate and the PDC layer. As previously explained, PDC cutter diameters have been limited to 19 mm to obviate this stress problem when used in rotary drill bits.
In one aspect, the invention includes a drill bit having a bit body including at least one blade thereon, and at least one polycrystalline diamond compact cutting element disposed on the blade. The polycrystalline diamond compact cutting element has a diameter between 19.0 mm and 25.0 mm.
In one aspect, the invention includes a drill bit having a bit body including at least one blade thereon, and at least one polycrystalline diamond compact cutting element disposed on the blade, wherein the polycrystalline diamond compact cutting element has a non-planar interface between a substrate and a diamond layer, and the polycrystalline diamond compact cutting element has a diameter between 19.0 mm and 25.0 mm.
In one aspect, the invention includes a drill bit having a bit body including at least one blade thereon, and at least one polycrystalline diamond compact cutting element disposed on the blade, wherein the polycrystalline diamond compact cutting element has an elliptical shape, and the polycrystalline diamond compact cutting element has a major axis diameter between 19.0 mm and 25.0 mm.
In one aspect, the invention includes a drill bit having a bit body including at least one blade thereon, and at least one polycrystalline diamond compact cutting element disposed on the blade. The cutting element has a non planar interface between a substrate and a diamond table thereof, and has a diameter greater than 19.0 mm.
In one aspect, the invention includes a drill bit having a bit body including at least one blade thereon, and at least one polycrystalline diamond compact cutting element disposed on the blade. The polycrystalline diamond compact cutting element has a diamond layer with a thickness greater than 0.140 inches. In some embodiments, the diamond table thickness is between 0.14 and 0.20 inches. The polycrystalline diamond compact cutting element in some embodiments has a diameter between 19.0 mm and 25.0 mm.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.